Decoupled electronic braking systems are being increasingly used in hybrid vehicles, enabling dynamic braking and/or flexibility in adjusting pedal response on the basis of demand.
In a decoupled braking system, the actuator that generates pressure in the hydraulic brake circuit is not directly controlled by pedal thrust, transmitted to the thrust rod by the control rod, but by an electronic signal generated by this pedal thrust movement. The signal, therefore, controls the actuator as a function of the braking request. Because of this physical decoupling, because the actuator cannot directly apply a response to the thrust rod and control rod, representing the response of the brake circuit, a brake simulator replaces it and imitates the response of the conventional braking system in response to the brake pedal.
In other words, in such systems the extremity of the control rod connected to the brake pedal is directly connected to a hydraulic thrust rod sliding inside the brake actuator, unlike conventional systems in which the actuator rod is connected to a pneumatic or electric brake booster component, which transmits the input force amplified by the components of the actuator unit. In this way, the sliding hydraulic component and the guide characteristics are directly subjected to all the forces coming from the pedal when the driver applies them or releases the pedal in different braking situations. Such components are, typically, much more sensitive to wear and malfunction than those of a conventional brake booster.
Additionally, in the absence of an intermediary brake booster between the brake pedal and the hydraulic components of the actuator, the transverse loads transmitted by the pedal housing to the hydraulic components by means of the control rod lead to premature wear, resulting in premature leakage of the seal components of the hydraulic circuit.
The control rod of a brake actuator, such as a pneumatic or electromechanical brake booster, requires a certain degree of freedom to operate, according to the kinematic needs imposed by the movement of the brake pedal actuated by the driver.
The actuator is fixed at its base to the firewall separating the vehicle's passenger compartment from the engine compartment, and the control rod crosses an opening realized in the firewall so it can be connected to the brake pedal or its housing.
In the case of an actuator consisting of a pneumatic brake booster, because of its internal structure, the control rod is naturally aligned along the axis of the thrust rod whenever it is still free, before installation of the actuator with the control rod in the vehicle and attachment of its second extremity to the brake pedal, the first being connected to the brake booster control device by a ball joint connector.
But, in the case of decoupled actuators, the control rod is not naturally maintained along the axis of the thrust rod. It can pivot freely within the solid angle defined by the characteristics of the shape of the thrust rod. However, to install the brake actuator in the vehicle, the operator must first pass the extremity of the control rod through an opening in the firewall, then hold the base of the actuator against the firewall and attach it to this with bolts.
In the case of electromechanical or electrohydraulic actuators, this installation is relatively difficult due to the very freedom of movement of the control rod with respect to the actuator, because the control rod pivots from its own weight and does not remain in the axis of the thrust rod. Therefore, the operator must feel around in order to pass the rod through the opening in the firewall.
To this is added the difficulty of access inside the vehicle engine compartment and the discomfort of the operator when installing this actuator. This results in a relatively lengthy and, therefore, costly operation as well as risking damage to the contacts as a result of direct impact with the surroundings.